Thermal Reduction of Hexavalent Chromium in Oxidic Solids
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Solution Overview
Problem
Current methods for reducing hexavalent chromium (Cr(VI)) in chrome ore residues, such as those produced during chromite processing, are inefficient, leading to environmental contamination and the need for hazardous waste management, as they either fail to completely convert Cr(VI) to Cr(III) or introduce additional pollutants like sulfur compounds.
Innovation Solution
A thermal reduction process using carbon-containing liquid compounds like glycerin or polyethylene glycol, which are mixed with oxidic solids containing Cr(VI), treated under a protective atmosphere at high temperatures, and then cooled to ensure complete conversion of Cr(VI) to Cr(III), thereby reducing the Cr(VI) content to below detectable limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reduction methods (FeSO4, SO2, H2S) are used to reduce Cr(VI) in chrome ore residues, then some Cr(VI) is converted to Cr(III), but the reduction is incomplete and additional pollutants (sulfur compounds) are introduced
Solution Approach 1:
The patent changes the chemical composition parameters of the reducing agent from conventional options (FeSO4, SO2, H2S) to carbon-containing compounds with specific carbon-to-chromium ratios (C:Cr from 2:1 to 10:1). This parameter change enables complete reduction of Cr(VI) without introducing sulfur compounds, as the carbon-based reducing agents (coke, charcoal, wood chips, sugar, starch) decompose to form CO and CO2 which reduce Cr(VI) to Cr(III) without residual pollution.
Solution Approach 2:
The patent employs inexpensive, readily available carbon-containing materials (coke, charcoal, wood chips, sugar, starch) as reducing agents. These materials are consumed completely during the reduction process, leaving no persistent harmful residues. The carbon-based agents are cheaper and more environmentally friendly than conventional reducing agents, achieving complete Cr(VI) reduction while avoiding long-term pollution issues.
2Ease of manufacture
If chrome ore residue is landfilled without treatment, then hazardous waste management is required, but Cr(VI) slowly dissolves into groundwater and soil causing environmental contamination
Solution Approach 1:
The patent converts the harmful Cr(VI) in chrome ore residue into beneficial Cr(III) through reduction treatment. The treated residue, now with Cr(VI) reduced to Cr(III), can be safely reused in construction materials (cement, concrete, bricks, tiles) rather than requiring landfill disposal. This transforms a hazardous waste problem into a valuable resource for the building materials industry, eliminating both disposal costs and environmental contamination risks.
3Quantity of substance
If leaching is performed to remove water-soluble Cr(VI), then some Cr(VI) is removed, but water-insoluble or water-poorly soluble Cr(VI) remains and cannot be obtained with economically justifiable effort
Solution Approach 1:
The patent changes the removal mechanism from physical leaching (water-based dissolution) to chemical reduction (carbon-based reduction at elevated temperatures). This parameter change enables the conversion and stabilization of both water-soluble and water-insoluble Cr(VI) forms into Cr(III), achieving complete removal of hexavalent chromium regardless of its initial solubility. The process is economically viable as it uses inexpensive carbon-containing materials and can be performed in standard industrial equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process effectively reduces Cr(VI) to Cr(III) in chrome ore residues, making the treated material non-hazardous and suitable for reuse in building materials or alloy production, with minimal environmental impact and no introduction of sulfur compounds.
Implementation Method 1
A thermal reduction process using carbon-containing liquid compounds like glycerin or polyethylene glycol, which are mixed with oxidic solids containing Cr(VI), treated under a protective atmosphere at high temperatures
Implementation Method 2
the carbon-containing compound prefers to decompose at temperatures > 150 °C instead of evaporating
Data Source
AI summary
A method for reducing hexavalent chromium in oxidic solids containing the steps: a) mixing the oxidic solid, containing Cr(VI), with a carbon-containing liquid compound in the range of 20 to 100?C; b) treating the mixture obtained according to a) under a protective atmosphere in an indirectly heated reactor at a temperature of 700?C to 1100?C, particularly preferably at a temperature of 800?C to 1000?C; c) cooling the reaction product obtained according to b) under a protective atmosphere to at least 300?C, preferably to at least 150?C.